Methods and apparatus for coupling gas turbine engine components

ABSTRACT

A method facilitates assembling a gas turbine engine assembly including at least a first member and a second member. The method comprises inserting a threaded fastener through an opening formed in a flange, and providing at least one shank nut including a flanged mating end, an opposite non-mating end, and a body extending therebetween. The body includes an internal surface, an external surface, and a centerline extending between the body ends. The flanged mating end includes a substantially planar exterior surface that is aligned perpendicularly to the centerline and an annular groove that extends from the exterior surface at least partially towards the non-mating end. The method also comprises securing the assembly together such that the mating end is positioned flush against the flange and such that the threaded fastener extends at least partially into a bore extending through the shank nut and defined by the shank nut internal surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No. 10/840,776, filed May 6, 2004, now U.S. Pat. No. 7,296,957, which is hereby incorporated by reference and is assigned to assignee of the present invention.

BACKGROUND OF THE INVENTION

This invention relates generally to coupling assemblies, and, more particularly, to methods and apparatus for coupling gas turbine engine components together.

At least some known mechanical coupling assemblies used to couple gas turbine components together include a threaded fastener and a threaded connector. More specifically, within at least some known applications, the threaded fastener is inserted through an opening formed in a flange prior to a connector being threadably coupled to it for securing a component to the flange. At least some known flange openings are counter-bored to enable a portion of the threaded fastener to remain recessed with respect to an external surface of the flange after the fastener is coupled to the flange.

As the connector is threadably tightened to the fastener, clamping loading is induced to the flange. However, when counter-bored openings are used, at least a portion of the clamp loading induced to the flange is carried by the thinner portions of the flange that define the counter-bore. Over time, the uneven load pattern stresses induced within the flange may cause the edges of the fastener opening within the flange to roll inward and away from the threaded connector, in a condition known as “bolthole rolling.” Bolthole rolling may cause additional stresses to be induced to the flange which over time may cause a premature failure of the flange.

BRIEF DESCRIPTION OF THE INVENTION

In one aspect, a method for assembling a gas turbine engine assembly including at least a first member and a second member is provided. The method comprises inserting at least one threaded fastener through a fastener opening formed in a flange extending from the first member, and providing at least one shank nut including a flanged mating end, an opposite non-mating end, and a body extending therebetween, wherein the body includes an internal surface, an external surface, and a centerline extending between the first and second ends, and wherein the flanged mating end includes a substantially planar exterior surface that is aligned perpendicularly to the centerline and an annular groove that extends from the exterior surface at least partially towards the non-mating end. The method also comprises securing the assembly together such that the flanged mating end is positioned flush against the flange and such that the threaded fastener extends at least partially into a bore extending through the shank nut and defined by the shank nut internal surface.

In another aspect, a shank nut for mating with a threaded mating component is provided. The nut includes a flanged mating end, an opposite non-mating end, and a body extending therebetween. The flanged mating end includes an exterior surface that is substantially planar. The body includes an internal surface, an external surface, and a centerline extending between the first and second ends. The internal surface defines a bore extending between the first and second ends. The bore is sized to receive at least a portion of the mating component therein. The mating end exterior surface is perpendicular to the body centerline and includes a groove extending at least partially circumferentially around the body bore. The groove extends axially from the mating end exterior surface at least partially towards the nut non-mating end.

In a further aspect, a coupling assembly for a gas turbine engine is provided. The coupling assembly includes a flange including at least one fastener opening extending therethrough, and a shank nut for mating with the threaded fastener. The at least one fastener opening is sized to receive at least a portion of a threaded fastener therethrough. The shank nut includes a flanged mating end, an opposite non-mating end, and a body extending therebetween. The flanged mating end includes a substantially planar exterior surface. The body includes an internal surface and an external surface. The body also includes a centerline extending between the first and second ends. The internal surface defines a bore extending between the first and second ends. The bore is substantially concentrically aligned with respect to the body and is sized to receive at least a portion of the threaded fastener therein. The mating end exterior surface is perpendicular to the body centerline and includes an annular groove extending generally axially from the mating end exterior surface and at least partially towards the shank nut non-mating end. The flange is coupled against the shank nut mating end.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a cross sectional view of a portion of an exemplary embodiment of a coupling assembly; and

FIG. 2 is an enlarged perspective view of the threaded connector used with the coupling assembly shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 a cross sectional view of a portion of an exemplary embodiment of a coupling assembly 10 including a threaded connector or shank nut 12. FIG. 2 is a perspective view of threaded connector 12 that is used with coupling assembly 10. Specifically, coupling assembly 10 includes at least one flange 20, shank nut 12, and a threaded fastener (not shown). In one embodiment, the threaded fastener is a threaded bolt that is threadably coupled to shank nut 12, as described in more detail below. Coupling assembly 10 is used to securely couple components together, such as gas turbine engine components. In the exemplary embodiment, coupling assembly 10 is used to couple adjacent mating portions of a rotor shaft 14 together. In one embodiment, rotor shaft 14 is a multi-piece rotor shaft that is used with a CF6-80 gas turbine engine commercially available from General Electric Aircraft Engines, Cincinnati, Ohio.

In the exemplary embodiment, each shaft portion 14 includes a coupling flange 20 that extends radially outward from an external surface 21 of shaft 14 to enable adjacent portions of shaft 14 to be coupled together. It should be noted that in FIG. 1, although only one shaft portion 14 is illustrated, each shaft portion 14 includes a coupling flange or other known coupling means, that enables shaft portions 14 to be coupled together. Flange 20 includes a mating surface 22, an opposite coupling surface 24, and at least one fastener opening 26 extending therebetween. In the exemplary embodiment, fastener opening 26 is extends through a counter-bored portion 28 of flange 20, such that a sidewall 30 defining counter-bored portion 28 and opening 26 is obliquely oriented with respect to surfaces 22 and 24. Accordingly, a thickness T of flange 20 measured between coupling surface 24 and a sidewall 30 is variable across counter-bored portion 28.

Shank nut 12 includes a flanged mating end 40, an opposite non-mating end 42, and a generally cylindrical body 44 extending therebetween. In the exemplary embodiment, body 44 has a substantially circular cross-sectional profile. In alternative embodiments, body 44 has other cross-sectional shapes. Body 44 has an external surface 50, an internal surface 52, and a centerline 55 that extends between ends 40 and 42. Internal surface 52 defines a bore 54 that extends between body ends 40 and 42. In the exemplary embodiment, bore 54 is concentrically aligned with respect to body 44 and has a diameter D_(B) that is substantially constant through bore 54. Internal surface 52 is threaded and includes a plurality of threads 60 that extend between body ends 40 and 42. Diameter D_(B) is sized to receive at least a portion of the threaded fastener therein.

In the exemplary embodiment, shank nut external surface 50 is tapered from flanged mating end 40 at least partially towards non-mating end 42, such that a wall thickness T_(W) of body 40 measured between body surfaces 50 and 52 is at least partially variably between body ends 40 and 42. More specifically, in the exemplary embodiment, external surface 50 is tapered from a hook 70 extending from body 40 at least partially towards non-mating end 42.

In the exemplary embodiment, hook 70 extends radially outward from body 44 such that an outer end 71 of hook 70 is positioned a distance D₁ forward of an end surface 72 of mating end 40. Distance D₁ enables hook 70 to extend radially outward of an outer edge 74 of flange 20 such that hook 70 provides an anti-rotation feature to shank nut 12, as described in more detail below. In the exemplary embodiment, hook 70 includes a scallop 76 which enables shank nut 12 to be easily visually distinguishable from other threaded connectors. In alternative embodiments, shank nut 12 does not include hook 70.

A chamfer 80 is formed along mating end 40 at the edge 82 formed between body external surface 50 and end surface 72. In the exemplary embodiment, chamfer 80 is positioned diametrically opposite hook 70 and is formed substantially parallel to the width W_(H) of hook 70 rather than following the circular arc of edge 82. Because of installation space limitations, in the exemplary embodiment, chamfer 80 enables shank nut 12 to be formed with a larger flange radius R_(F) at mating end 40. In alternative embodiments, shank nut 12 does not include chamfer 80.

In the exemplary embodiment, shank nut 12 also includes a shank barrel 90 extending outward from mating end 40. Specifically, in the exemplary embodiment, shank barrel 90 is substantially cylindrical and extends a distance D₂ from end surface 72 to a outer edge 92. Distance D₂ enables shank barrel 90 to be swaged or outwardly flared such that shank nut 12 is retained in an axial direction against flange 20 during assembly by shank barrel 90, as is described in more detail below. Shank barrel 90 has a diameter D₄ defined by an outer surface 96 of shank barrel 90 that is smaller than an inner diameter D₅ of flange fastener opening 26 adjacent flange coupling surface 24.

A groove 100 is defined within mating end 40 and extends a distance D₆ axially inward from end surface 72. In the exemplary embodiment, groove 100 is annular and extends circumferentially around shank barrel 90 and bore 54. In an alternative embodiment, groove 100 extends only partially circumferentially around barrel 90. In another alternative embodiment, mating end 40 includes a plurality of grooves defined therein. As is described in more detail below, groove 100 facilitates redistributing clamping loading radially outward from shank nut centerline 55 when shank nut 12 is securely coupled in position.

During assembly of rotor shaft 14, initially shank nut 12 is positioned adjacent flange 20. Specifically, initially shank nut 12 is positioned such that shank nut mating end 40 is against flange coupling surface 24. Accordingly, shank barrel 90 extends at least partially through flange fastener opening 26. Shank barrel 90 is then swaged or flared using a known flaring tool such that shank barrel 90 is forced outwardly against flange fastener opening sidewall 30. Accordingly, once swaged, shank barrel 90 facilitates retaining shank nut 12 in an axial direction in position relative to, and against, flange 20.

A component to be coupled to rotor shaft 14 is then positioned adjacent shaft 14 such that a flange extending from that component is against the mating surface 22 of flange 20. A threaded fastener is then inserted through the first component flange and through flange 20. More specifically, as the fastener is extended through flange 20, the fastener is rotated to be threadably coupled to shank nut 12. Because hook 70 extends radially outward from an outer edge 74 of flange 20, hook 70 facilitates preventing nut 20 from rotating as the threaded fastener is torqued within nut 12.

Continued rotation of the fastener enables shank nut 12 to induce a clamping force to flange 20 such that the components of rotor shaft 14 are securely coupled together. More specifically, shank nut groove 100 facilitates redistributing clamping loading radially outward from shank nut centerline 55 such that the reaction loading is not induced through counter-bored portion 28, but rather is instead induced through a portion 100 of flange 20 that has a thickness T₁ that is thicker than that any thickness T measured within counter-bored portion 28. Moreover, the additional material thickness T₁ of flange portion 100 facilitates structurally enhancing the stiffness of flange 20 such that bolt rolling within flange fastener opening 26 is facilitated to be reduced as a result of groove 100. Furthermore, the tapering of shank nut external surface 50 facilitates enabling the clamp load to more easily pass between the nut threads 60 and mating surface 72.

After the threaded fastener has been securely coupled within shank nut 12, shank nut non-mating end 42 is crimped against the threaded fastener. Crimping end 42 facilitates preventing shank nut 12 from unthreading from the threaded fastener, such that end 42 provides a self-locking feature to nut 12.

The above-described coupling system is a cost-effective and reliable means for coupling components together. The shank nut includes an annular groove which displaces the mating surface of the nut radially outward, such that clamp loading is redistributed radially outward from the nut bore. Accordingly, the clamp loading is carried by a thicker portion of the mating flange such that stresses induced to the flange, and/or bolt rolling of the fastener opening within the flange, are facilitated to be reduced. As a result, the shank nut facilitates securely coupling components together in a cost-effective and reliable manner

Exemplary embodiments of coupling assemblies are described above in detail. The assemblies are not limited to the specific embodiments described herein, but rather, components of each assembly may be utilized independently and separately from other components described herein. For example, each shank nut component can also be used in combination with other coupling assemblies.

While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims. 

1. A method for assembling a gas turbine engine assembly having a rotational axis, the gas turbine engine assembly including a flange that has a mating surface that extends substantially perpendicular to the rotational axis and a fastener opening that extends substantially parallel to the rotational axis, said method comprising: inserting a threaded fastener through the fastener opening; providing a shank nut including a mating end, an opposite non-mating end, and a body extending between the mating end to the non-mating end, wherein the body comprises an internal surface, an external surface, and a centerline extending from the mating end to the non-mating end, the mating end including a substantially planar exterior surface that is aligned substantially perpendicular to the centerline and an annular groove that extends from the exterior surface at least partially towards the non-mating end said body further comprises a hook extending outward from said external surface, said hook is a distance from said mating end, wherein at least a portion of said body is chamfered adjacent said mating end and diametrically opposite said hook with respect to said centerline; and securing the fastener to the shank nut such that the exterior surface is positioned against the mating surface to define an open space between the annular groove and the mating surface.
 2. A method in accordance with claim 1 wherein securing the fastener to the shank nut further comprises securing the fastener to the shank nut such that the annular groove facilitates reducing an amount of reaction loading induced to the flange.
 3. A method in accordance with claim 1 wherein securing the fastener to the shank nut further comprises positioning the shank nut against the flange prior to inserting the fastener through the fastener opening such that a shank barrel extending from the mating end extends at least partially through the fastener opening.
 4. A method in accordance with claim 3 wherein positioning the shank nut against the flange prior to inserting the fastener through the fastener opening further comprises outwardly flaring an end of the shank barrel such that the shank barrel axially retains the shank nut to the flange.
 5. A method in accordance with claim 1 wherein securing the fastener to the shank nut further comprises securing the shank nut in position relative to the flange such that said hook extending from the external surface substantially prevents rotation of the shank nut relative to the flange.
 6. A method in accordance with claim 1 wherein securing the fastener to the shank nut further comprises crimping the non-mating end to provide a self-locking mechanism. 